CPS 100, Fall COMPSCI 100, Fall 2011 Owen Astrachan w/ Michael Hewner

CPS 100, Fall Data into Information and Knowledge Computer Science

CPS 100, Fall What can you do with Compsci?

CPS 100, Fall What can you do with Compsci?

CPS 100, Fall What can you do with Compsci?

CPS 100, Fall What can you do with Compsci?

CPS 100, Fall What can you do with Compsci?

CPS 100, Fall What can you do with Compsci?

CPS 100, Fall What is Computer Science? What is it that distinguishes it from the separate subjects with which it is related? What is the linking thread which gathers these disparate branches into a single discipline? My answer to these questions is simple --- it is the art of programming a computer. It is the art of designing efficient and elegant methods of getting a computer to solve problems, theoretical or practical, small or large, simple or complex. C.A.R. (Tony)Hoare

CPS 100, Fall What will you experience?

CPS 100, Fall Programming != Computer Science l What is the nature of intelligence? How can one predict the performance of a complex system? What is the nature of human cognition? Does the natural world 'compute'? l It is the interplay between such fundamental challenges and the human condition that makes computer science so interesting. The results from even the most esoteric computer science research programs often have widespread practical impact. Computer security depends upon the innovations in mathematics. Your Google search for a friend depends on state-of-the-art distributed computing systems, algorithms, and artificial intelligence.

CPS 100, Fall Efficient design, programs, code Tradeoffs, Tradeoffs, Tradeoffs Object-oriented design and patterns. Software design principles transcend language, but … Engineer, scientist: what toolkits do you bring to programming? Mathematics, design patterns, libraries --- standard and others… Know data structures and algorithms. Trees, hashing, binary search, sorting, priority queues, greedy methods, graphs … Using the language: Java (or C++, or Python, or …), its idioms, its idiosyncracies

CPS 100, Fall Course Overview l There are details, see the course web pagecourse web page  Midterms and final are open book, what does that mean?  APTs: Algorithmic Problem-solving and Testing Weekly small programming assignments, tested online  Programming assignments: solo, paired, … l Why should you come to class?  Meet people, learn things, participate in a community  Provide help, get help, wonder, dance, think  Participate in graded exercises that affect your final grade l Why is this course so great?  Because you’re in it

CPS 100, Fall What's in Compsci 100? l Understanding tradeoffs: reasoning, analyzing, describing…  Algorithms  Data Structures  Programming  Design l Programming using Java  Tools: Eclipse, JDK, Libraries, …  Ideas: Design Patterns, OOP, Agile programming, …  Engineering and analyzing designs and programs  Using mathematical and scientific techniques  Scaling solutions

CPS 100, Fall Questions If you gotta ask, you’ll never know Louis Armstrong: “What’s Jazz?” If you gotta ask, you ain’t got it Fats Waller: “What’s rhythm?” What questions did you ask today? Arno Penzias

CPS 100, Fall Tradeoffs Simple, elegant, quick, efficient: what are our goals in programming? What does XP say about simplicity? Einstein? How do we decide what tradeoffs are important? Tension between generality, simplicity, elegance, … Fast programs, small programs, run anywhere- at-all programs. Runtime, space-time, your time, CPU time… Programming, design, algorithmic, data- structural

CPS 100, Fall Language

CPS 100, Fall From Blog to Scientific Visualization l Text Cloud aka Tag Cloud?  Number of occurrences/emphasis indicated by size of word  Great visual/statistic: l What is involved with generating tag clouds?  Steps? Issues?  We will look at code to generate the tag cloud, but we'll look at simpler code first

CPS 100, Fall

CPS 100, Fall Problem Solving and Programming l How many words are in a file?  What’s a word?  What’s a file?  How do we solve this: simply, quickly, …? What’s the best we can do? Constraints? l How many different/unique words are in a file?  How is this related to previous task? l How many words do two files have in common?  Spell-checking, Google did you mean..?

CPS 100, Fall Fast, cheap, out-of-control? l This is valid and correct Java code, questions? import java.util.*; import java.io.*; public class SimpleUnique { public static void main(String[] args) throws FileNotFoundException{ Scanner s = new Scanner(new File("/data/kjv10.txt")); s.useDelimiter("\\Z"); String all = s.next(); String[] words = all.split("\\s+"); TreeSet set = new TreeSet (); set.addAll(Arrays.asList(words)); System.out.printf("total #: %d, unique #: %d\n", words.length,set.size()); } total #: , unique #: 34027

CPS 100, Fall Pythonic WordCounting This is valid and correct Python code, questions? def countWords(filename): file = open(filename) str = file.read() words = str.split() unique = set(words) print "filename: ", filename print "total # words = ",len(words) print "unique # words = ",len(unique) countWords('/data/kjv10.txt') filename: /data/kjv10.txt total # words = unique # words = 34027

CPS 100, Fall How fast is fast? How cheap is cheap? l How do we measure how fast the code/design is?  Can we implement this design in C++?  Can we implement this in Ruby? l We want a measure that’s independent of language?  What are we measuring?  How do we express answer?  Units? Best case? Average? Worst? l What is answer using recognized terminology? 

CPS 100, Fall What is Computer Science? l Computer science is no more about computers than astronomy is about telescopes. Edsger Dijkstra l Computer science is not as old as physics; it lags by a couple of hundred years. However, this does not mean that there is significantly less on the computer scientist's plate than on the physicist's: younger it may be, but it has had a far more intense upbringing! Richard Feyneman

CPS 100, Fall Some Java Vocabulary and Concepts l Java is a (statically) typed language  Every variable/object has a type that's defined at compile time (compare Python)  More typing, but more errors caught before runtime l Java is an object-oriented language  All code is in a class and all code inside function/method  Classes are also types, so variables/objects extendible  We will see interfaces and inheritance later  Classes have instance variables, methods local variables l Java has different 'types' primitive and Object/class. This is for efficiency, but it's sometimes confusing

CPS 100, Fall MoreJava Vocabulary and Concepts l Java has a huge standard library  Organized in packages : java.lang, java.util, javax.swing, …  API browseable online, but Eclipse IDE helps a lot l Java methods have different kinds of access inter/intra class  Public methods …  Private methods …  Protected and Package methods … l Primitive types (int, char, double, boolean) are not objects but everything else is literally an instance of class Object  foo.callMe();

CPS 100, Fall Solving problems, writing code l APT: AccessLevel APT: AccessLevel  Understand the problem, know how to solve an instance  Ideas? Caveats? l Writing code to implement proposed solution  Will it run? In time? Constraints? Look before you code  How will we test the solution? When to start testing? l What’s the green dance and when do we do it?  Satisfaction of finishing something  Knowing when to stop when you’re not making progress  Leveraging community wisdom

CPS 100, Fall Structuring Information: ideas & code l Is an element in an array, Where is an element in an array?  DIY: use a loop  Use Collections, several options  Tradeoffs? public boolean contains(String[] list, String target){ for(String s : list){ if (s.equals(target)) return true; } return false; } public boolean contains(String[] list, String target){ return Arrays.asList(list).contains(target); } public boolean contains(String[] list, String target){ return new HashSet (Arrays.asList(list)).contains(target); }

CPS 100, Fall Basic data structures and algorithms l Arrays are typed and fixed in size when created  Don't have to fill the array, but cannot expand it  Can store int, double, String, Object, … l ArrayList (and related interface List) grows s needed  Stores objects, not primitives Autoboxing in Java 5 facilitates int to/from Integer conversion Store an int in an ArrayList, get one out Can’t convert entire ArrayList to array for int, can for String, why?  ArrayList objects grow themselves intelligently java.util package has lots of data structures and algorithms  Use rather than re-implement, but know how do to do both

CPS 100, Fall Who is Alan Perlis? l It is easier to write an incorrect program than to understand a correct one l Simplicity does not precede complexity, but follows it l If you have a procedure with ten parameters you probably missed some l If a listener nods his head when you're explaining your program, wake him up l Programming is an unnatural act l Won first Turing award

CPS 100, Fall Analysis of StaticSimpleWords.java l How are variables used?  What types are there, definitions, re-used variables,  What is a File, a Scanner, a String[], a HashSet, a … l How are strings and values printed?  What is System.out? How is it used? l Why is there a FileNotFoundException thrown from main?  What is an exception, how do we handle them? l How are statements organized, how is whitespace used?

CPS 100, Fall Who takes Compsci 100 Now?